Conventional automobiles have an inherent aerodynamic instability which becomes dangerous under certain conditions. A slight crosswind, or a slight angle between the vehicle heading and its direction of travel (a yaw angle), creates aerodynamic forces on the vehicle which tend to increase the yaw angle, which in turn tends to increase the aerodynamic forces, and so on, so that when the tires have insufficient grip on the road (as on an icy bridge), the car will spin around.
This aerodynamic instability can be avoided by installing vertical stabilizing fins near the aft end of the vehicle, as described in U.S. Pat. No. 2,665,137. In addition to providing directional stability, such vertical airfoils have a fuel-saving function, as taught by U.S. patent application Ser. No. 223,230 filed by the inventor of the present invention. In the presence of a crosswind, vertical fins develop a forward thrust as a result of a suction region along the fin leading edge. Although vertical fins provide the important benefits of enhanced stability and fuel efficiency, they tend to develop large rolling moments in strong crosswinds, leading to an undesirable lateral tilting of the vehicle, and possibly even overturning. The possibility of overturning is increased for fins with inclined leading edges, since the suction along the inclined leading edges gives rise to lifting forces.
U.S. Pat. No. 3,804,428, granted to the inventor of the present invention, describes a vehicle with an inverted U-shaped or ring-shaped airfoil. Airfoils of this configuration have helped eliminate aerodynamic losses normally encountered at the tips of vertical airfoils. However, these airfoils have a center of lateral aerodynamic pressure which is substantially above the vehicle center of gravity and above the lowest point on the airfoil. As a result, these airfoils also tend to develop large rolling moments in strong crosswinds.
It is an object of the present invention, therefore, to provide an improved energy-efficient vehicle that will carry people in comfort and safety. It is another object of this invention to provide a stabilizing device for a surface transport vehicle which will promote directional stability and fuel conservation while minimizing the lateral rolling of the vehicle in a crosswind and the danger of lateral overturning.